1. Field of the Invention
The present invention relates to a detection device and, more particularly, to a device for detecting a bad editing in image signals.
2. Description of the Related Art
Due to the bandwidth limitation, the current television signals are transmitted and displayed by an interlaced manner. As shown in FIG. 1, an image frame is generated by interlacing one even field 11, 13 and one odd field 10, 12, wherein the odd field 10, 12 contains only odd lines of the image frame, and the even field 11, 13 contains only even lines of the image frame. In order to improve the vertical resolution, next generation televisions require a line doubler to perform a frequency multiplication process to increase the vertical resolution. One of the simplest frequency multiplication processes involves directly combining two adjacent fields (an odd field and another even field) to form a progressive scan frame. However, due to a time difference between the two fields, the progressive scan frame yields zigzag patterns on moving objects in the image.
In order to avoid the above-mentioned problem, an advanced line doubler is provided with a motion detector to detect the moving objects in the image, and applies an inter-field interpolation of a de-interlaced process to the still parts of an image, and an intra-field interpolation of the de-interlaced process to the moving parts of an image.
Another frequency multiplication process is achieved by determining whether the image source is from a film. It is known that a film is formed by recording 24 frames per second. Thus, if the film is to be displayed following the NTSC television standard, the 24 frames per second must be transformed into 60 fields per second. As shown in FIG. 2, this transformation technique is known as “3:2 pull down”; in other words, two continuous frames of the film are respectively transformed into 3 fields and 2 fields. For example, a frame 14 of the film is transformed into a field 18 (an odd field), a field 19 (an even field) and a field 20 (an odd field), and a frame 15 of the film is transformed into a field 21 (an even field) and a field 22 (an odd field), and so on. Therefore, if the image source is recognized as originally from a film, a perfect output, without any zigzag effect, can be obtained by combining only the odd field and the even field originally from the same film frame, and thus the moving object can be provided with the highest possible vertical resolution.
In order to determine the type of image resource, a prior art technique utilizes frame motion data or field motion data to determine whether the image source is from a film. FIG. 3 shows a frame motion detector 31 providing frame motion data. As shown in FIG. 3, every frame motion detector 31 is used for detecting whether two continuous odd fields or even fields are identical; if they are, a “0” is outputted; if they are not, a “1” is outputted. Therefore, if the television image is from a still picture, regardless of whether the image source is from a film or a video, the frame motion detector 31 continuously outputs a sequence “00000,00000, . . . ”; if the television image is from a moving video, the frame motion detector 31 continuously outputs a sequence “11111,11111, . . . ”; if the television image is from a moving film, the frame motion detector 31 continuously outputs a sequence “01111,01111, . . . ”.
According to the output from the frame motion detector 31, a state transition diagram of film detection, as shown in FIG. 4, is utilized for determining whether the television image is from a film processed by 3:2 pull down. In the state transition diagram, states A˜F are corresponding to the video mode, and states G˜K are corresponding to the film mode. As shown in the drawings, the state A is an initial state of the state transition diagram. When the input sequence is “01111”, the state will transit to state E, and a counter 41 is incremented. When the count value of the counter 41 exceeds a threshold value, the state transits from E to G, i.e., from the video mode to the film mode.
If the image is processed by 3:2 pull down, the frame motion detector 31 outputs “01111” or “0000”. After the frame motion detector 31 outputs a predetermined number of the sequence “01111”, the state of the state transition diagram transits from the video mode to the film mode. Under the film mode, as long as the input remains “0XXXX”, the state remains in the film mode.
The prior art technique can detect whether the image resource is from a film so as to provide a perfect frequency multiplication process. However, a bad editing of the film will impair the 3:2 pull down process, which causes zigzag effect in the television image. As shown in FIG. 5, fields 1˜8 are from a film segment A, and fields 9˜16 are from another film segment B. Due to a bad editing in the film segment B, field 9 and the following fields are not consistent with the 3:2 pull down process. Please refer again to FIG. 4 and the state transition diagram can only determine that the image is fit to the film mode at field 11. Therefore, when the field 9 is used as a basis to generate the television image, the field 9 and the field 10 originally from different film frames are combined into one image frame, and the television image incurs zigzag effect as a result.
In order to solve the above-mentioned problem, U.S. Pat. No 6,201,577 granted to Peter D. Swartz for a “Film source video detection” discloses a method of detecting bad editing on current television image. The method notifies a film detector to leave the film mode when there is a bad editing detected, so as to avoid combining two fields from different frames into an image frame. However, because the detection is performed on the current television image, when the bad editing is detected, the line doubler has already outputted an image frame with zigzag effect.
Therefore, it is desirable to provide a bad editing detection device for video signal to mitigate and/or obviate the aforementioned problems.